1. Field
The present disclosure relates to a semiconductor device, and more particularly, to a high electron mobility transistor.
A. 2. Description of the Related Art
Devices for controlling a current flow through ON/OFF switching, e.g., power devices, may be used for various power conversion systems. In such a power conversion system, the efficiency of a power device affects that of the whole system.
Power devices being commercialized currently are mostly classified into silicon-based power metal-oxide-semiconductor field-effect transistors (MOSFETs) or insulated gate bipolar transistors (IGBTs). However, due to the limits of silicon's physical properties and manufacturing processes, it is difficult to increase the efficiency of the silicon-base power devices. To overcome these limits, research and development for increasing conversion efficiency by applying the group III-V-based compound semiconductors into power devices are in progress. In a related development, high electron mobility transistors (HEMTs) using a heterojunction structure of compound semiconductors are in the spotlight.
Such a HEMT may include semiconductor layers having electrical polarization characteristics different from each other. In the HEMT, a semiconductor layer having relatively large polarizability may induce a 2-dimensional electron gas (2DEG) in the other semiconductor layer bonded to the semiconductor layer. Here, the 2DEG may have very high electron mobility.
If a gate voltage is 0 V in the HEMT, when the HEMT is in a normally-on state in which current flows due to low resistance between a drain electrode and a source electrode, current and power loss may occur. Thus, to turn the current between the drain electrode and the source electrode off, a negative voltage should be applied into the gate electrode. Recently, to solve the above-described limitation, a HEMT which includes a depletion formation layer or a recess structure under the gate electrode to realize a normally-off characteristic in which the current between the drain electrode and the source electrode is turned off when the gate voltage is 0 V is being studied.